1. Field of the Invention
The present invention concerns computer systems in general, and techniques for mounting PCBs to computer system chassis in particular.
2. Background Information
Mounting holes are provided in printed circuit boards (PCBs) to secure the PCBs to the computer system chassis they are mounted in. Typically, a PCB will be secured to it chassis using threaded fasteners, which are inserted into threaded holes or press-in threaded barrels (i.e., standoffs, such as Keenserts) disposed in the chassis. Generally, a manufacturer will specify a minimum separation dimension between the PCB and the chassis for the followings reasons: 1) to provide room for back-side component placement; 2) to provide a gap between protruding leads and the chassis sheet metal to avoid electrical short circuits; and 3) to provide sufficient engagement between screws and chassis-mounted, press-in threaded barrels.
Recent market demands have led the computer industry to develop computer systems with increased circuit densities. For example, many hardware vendors, such as Intel, Hewlett-Packard, IBM, Compaq, and Dell, offer high-density rack-mounted servers that enable a large number of servers to be housed within a single standardized rack. The chassis for these rack-mounted servers are configured to have a specific form factor that is designed to the standardized rack the servers are to be installed in. In one configuration, an ultra-thin form factor, known as the xe2x80x9c1Uxe2x80x9d form factor, is used. Under the 1U form factor, the chassis height for each server is only 1.75 inches.
In addition to increased circuit density, the components in these computer servers are operating at higher and higher frequencies. As a result, these components generate a large amount of heat, which must be removed from the chassis so that the components do not overheat. Generally, this heat is removed using forced air convection, which transfers the heat from the heat-producing circuit components by using one or more fans that are disposed within or coupled to the chassis to draw air through the chassis. In addition, heat sinks are often mounted to various high-power circuit components, such as CPUs.
In order to provide adequate flow passages and/or room for heat sinks in high-density configurations such as the 1U standard, it is necessary that space utilization is maximized, wherein no or minimal space is wasted. Thus, the distance between the PCB(s) and the chassis need to be accurately controlled. In addition, any mounting scheme that is used should not require changes in the manufacturing techniques used to make the PCBs, such as wave soldering, pick and place insertion, etc.